- One area in which obese and lean individuals may be different is how their bodies handle water balance and thirst. Studies done in animals suggest that individuals with greater body fat may tolerate periods without water better than lean animals. Other research has found a link between the ability to tolerate periods without water and increased body weight. Researchers are interested in studying whether the ability to tolerate periods without water and ability to feel thirst might differ in lean versus obese individuals.

Objectives:

- To evaluate the effects of water deprivation and feelings of thirst in lean and obese individuals.

Eligibility:

- Healthy individuals at least 18 years of age who are either lean (body mass index less than 26 kg/m(2)) or obese (body mass index at least 35 kg/m(2)).

Design:

Participants will be screened with a medical history, physical examination, and blood and urine tests.

Participants will spend the entire study (13 days) as inpatients at the National Institutes of Health Clinical Center.

Participants will have the following tests and procedures:

Body composition assessment (using low-level x-rays) to determine the percentage of fat tissue in the body.

Oral glucose tolerance test (similar to that often used to diagnose diabetes). Individuals who are suspected to have diabetes will not be allowed to continue with the study.

High salt infusion test, in which an infusion of saline (salt water) will be given for 2 hours and participants will respond to questions about how hungry and thirsty they feel during the procedure.

Water deprivation test, in which participants will go for 24 hours without water or food and respond to questions about how hungry and thirsty they feel.

24-hour stay in a metabolic chamber to determine how many calories participants burn in a day.

A series of questionnaires about participants' eating habits, feelings about food, and personal feelings, as well as computer-based tests involving the performance of various tasks.

Measurement of free-living energy using doubly-labeled water, in which participants will drink a sample of water with extra-heavy atoms of hydrogen and oxygen to evaluate the amount of water in the body.

Further study details as provided by National Institutes of Health Clinical Center (CC):

Primary Outcome Measures:

Measurement of how much water lean and obese volunteers drink after a water deprivation and hypertonic saline infusion

Secondary Outcome Measures:

Measurement of how thirsty lean and obese volunteers are after water deprivation and hypertonic saline infusion

Measurement of hormones related to salt and water balance in lean and obese volunteers after water deprivation and hypertonic saline infusion

Estimated Enrollment:

88

Study Start Date:

October 2010

Detailed Description:

The percentage of people with overweight / obesity in the United States has reached very high levels, with 65% of adults over the age of 20 being overweight. Recently, there have been a number of advances in our understanding of the underlying causes of obesity, including greater understanding of both the effects of the environment and effects that are hereditary (i.e., genetic).

One area in which obese versus lean individuals may be different is how their bodies handle water balance and thirst. Studies done in animals suggest that individuals with greater body fat may tolerate periods without water better than lean animals. Thus, at least in animals, others have found a link between ability to tolerate periods without water and increased body weight.

We are studying whether the ability to tolerate periods without water and ability to feel thirst might differ in lean versus obese individuals. To do so, we will ask lean and obese individuals to undergo tests that include a period of approximately 24 hours without drinking any water, and on a separate day a shorter period of an intravenous high salt solution infusion. We will be looking at how the ability to withstand thirst (dehydration), subsequent water intake (rehydration), changes in hormone levels during these periods, and behavioral and physiological responses to thirst and rehydration differ in lean versus obese individuals. We hope that the data gathered from this study will give us more information about important differences in how water balance is regulated in lean versus obese individuals. Understanding these questions may provide new insights into differences between lean and obese individuals.

Eligibility

Ages Eligible for Study:

18 Years to 50 Years

Genders Eligible for Study:

Male

Accepts Healthy Volunteers:

Yes

Criteria

INCLUSION CRITERIA:

Male.

Age 18-50 yrs to minimize hormonal influences on thirst perception in aging men.

BMI< 25 kg/m(2) for the lean group and BMI greater than 35 kg/m(2) for obese group (but weigh less than 350 pounds to accommodate the DXA scanner) for the obese group.

Healthy, as determined by medical history and physical examination, without the exclusions listed below:

Alcohol and/or current use of drugs (more than 2 drinks per day and regular use of drugs such as amphetamines, cocaine, heroin, or marijuana)

Psychiatric conditions or behaviors that would be incompatible with safe and successful participation in this study, including claustrophobia and eating disorders such as anorexia or bulimia nervosa

Contacts and Locations

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT01224704